Protective helmets which enclose substantially the entire skull of a wearer from the forehead to the base of the skull and which extend around the temple regions and even over portions of the face of the wearer are widely used by motorcyclists to provide the head protection required by law in many jurisdictions as well as a safety factor. Such helmets are, however, comparatively massive and, because of their size and weight have not been found to be satisfactory by bicyclists.
The helmets available for bicyclists have generally been of three types and are customarily of significantly lower cost than the motorcycle helmets which enclose more of the head of the wearer. The so-called soft shell helmet comprises a comparatively thick, substantially incompressible and resilient hard-foam shell which is generally constituted entirely of foamed polystyrene. The soft shell helmet is the least expensive of the three types (see the journal test, May 1992, page 80).
Both the price and weight are higher for so-called hard shell helmets in which over a foamed liner a second hard plastic shell is provided which makes the helmet more robust and also makes penetration of objects into the helmet more difficult.
A compromise between the hard shell helmet and the soft shell helmet is constituted by the so-called microshell model in which the foam shell is covered or coated by a thin plastic covering providing a hard surface for the exterior of the helmet (see test, op. cit. page 80).
The bicycling helmets of these three types, usually do not have any chin protection and in many cases may be only cosmetic with little ability to protect the rider. In other words in some cases the helmet may provide little if any protective effect.
The function of a protective helmet depends primarily upon its construction and the material used. It is the protective function which must be paramount if the helmet is to be successful.
One of the problems, however, is that the helmet is not always acceptable for children and young riders because the helmet may shift on the head, inadvertently fall off, or simply be uncomfortable (test, op. cit. page 81). Thus the two factors of greatest importance are the reliability of the helmet from a safety point of view and the acceptance of the helmet by the user, meaning that the helmet should not shift on the head or be displaced by forcible shaking of the head or the like (see test, op. cit. page 80).